Dendrocephalus riograndensis, Volcan, 2016

Dendrocephalus riograndensis View in CoL n. sp.

( Figs. 1–2 View Figure 1 View Figure 2 )

Type material. Holotype, male: Brazil. Rio Grande do Sul: Santa Vitória do Palmar, temporary pool, close to Mirim Lagoon , 32°46’41.5”S 52°40’26.6”W, 10 m elevation, 3 November 2015, M. V. Volcan & A.C. Gonçalves, MCP 3144 View Materials GoogleMaps . Allotype: female, same data as holotype, MCP 3145 View Materials GoogleMaps . Paratypes: 6 females, 6 males, same data as holotype, MCP 3146 View Materials GoogleMaps .

Type locality. ( Fig. 2G View Figure 2 ) The site is located in the Coastal Plain of Rio Grande do Sul, the southernmost state of Brazil, and in the Pampa Biome ( IBGE, 2004). This region is dominated by grasslands in flat terrain ( IBGE, 2004). The hydrography is represented by the Patos-Mirim Lagoon system, Laguna dos Patos Ecoregion, lying across southern Brazil and eastern Uruguay (Abell et al., 2008).

This area is subtropical, with an average temperature of 13°C in the coldest months (June and July) and above 22°C in the warmest months (January and February). The average annual rainfall (1200–1500 mm) is uniform in all seasons, but varies greatly in different years (Nobre et al., 1986).

Dendrocephalus riograndensis n. sp. was found in a small (~ 120 m ²), shallow (<60 cm depth) temporary pool, exposed to direct sunlight, near the margin of Mirim lagoon. The water tends to be humic. The pool is in a small depression, in grassland areas of private farms. The aquatic vegetation was abundant (especially submerged macrophytes), but D. riograndensis n. sp. was only observed in the deepest portions of the pool, where there was no vegetation.

Dendrocephalus riograndensis View in CoL n. sp. co-occurs with the annual fish Austrolebias charrua View in CoL Costa & Cheffe, 2001; an endangered endemic species in Brazil and Uruguay ( Loureiro et al., 2013; MMA, 2014). Dendrocephalus riograndensis View in CoL n. sp. suffers from the same problems that led A. charrua View in CoL to be considered endangered: habitat loss and fragmentation due to their natural habitat converted to rice agriculture.

Etymology. The name “ riograndensis ” refers to the state of Rio Grande do Sul where this species was discovered.

Diagnosis. ( Figs. 1 View Figure 1 , 2A–E View Figure 2 ) Typical Dendrocephalus . Male bearing eye spine; second antenna, proximal antennomere with medial projection, bearing small denticles; frontal appendage bearing several spines along the anterior margin, between primary branches; branch 1V anterior sub-branch acute, posterior sub-branch in subdistal position; branch 2V posterior surface deeply concave, bearing two nearly apical cell pads and one cell pad on medial surface; branch 2D sub-branch I greater than twice the length of sub-branch II; sub-branch I and II with medial longitudinal row of close set, fine spines, joining at branch 2D base; branch 2A apex podiform; thoracopod I with single medial spiniform process; thoracopod I mediodistal corner triangular; thoracopod I proximolateral margin greatly elongated, arcuate, spiniform projection.

Description. Average length of preserved material: 18.6 mm from apex of head to apex of telson (males averaging 18.8, n = 7; females averaging 18.4, n = 7).

Male. ( Fig. 1A View Figure 1 ) Anterolateral corner of head projecting over eyestalk base. Compound eye with posteroventral spine ( Figs. 1A View Figure 1 , 2A View Figure 2 ). First antenna filiform, approximately 60% length of second antenna. Antenna like appendage anterobasal to eyestalk, filiform, slightly longer than eyestalk peduncle.

Frontal (cephalic) appendage prominent, typical of genus ( Fig. 1A View Figure 1 ), when expanded reaching thoracomere X or XI. Frontal appendage basal trunk and primary branches anterior margin bearing six spines at bifurcation point, spines increasing in size from proximal to distal. Primary branch from bifurcation to branch 1V base twice as long as trunk, bearing four to six dorsal spines. Primary branch from branch 1V base to branch 2V base approximately one third length of primary branch from bifurcation to branch 1V base, bearing medial, longitudinal row of small spines, decreasing in size distally.

Branch 1V well developed, anterior sub-branch tapering to rounded apex, never tumid ( Fig. 1A View Figure 1 ). Peduncle length 40% anterior sub-branch, bearing two large, dorsal spines proximal to posterior sub-branch. Anterior sub-branch bearing numerous scattered proximally directed spines, distal of posterior sub-branch base. Posterior sub-branch originating midlength, length approximately 20% anterior sub-branch, bearing one subproximal spine.

Branch 2V thick, flattened, with numerous semiannulations ( Figs. 1A, B View Figure 1 ). Apex subcoiled posteriorly, bearing one apical and one subapical “knob structure” ( Pereira, 1983) or “cell pad” ( Margalef, 1961), with similar structure projecting distally from posterior surface, nearly in contact with apex. Medial margin bearing longitudinal row of projecting smooth lobes.

Branch 2D base broadly triangular ( Fig. 1A View Figure 1 ). Sub-branch I length subequal to primary branch from bifurcation to branch 1V, subcylindrical basally, tapering to acute apex. Sub-branch I anterior surface with longitudinal row of four large, long, recurved spines. Sub-branch I medial surface with longitudinal row of small, close set spines, extending from branch 2D base, to sub-branch I apex. Sub-branch I distal 50% covered in small scattered spines; apex tipped with single small spine. Sub-branch II length approximately 50% of sub-branch I, tapering to rounded apex. Sub-branch II posterior surface with longitudinal spine row, with proximal first two spines three to four times size and length of remaining spines. Sub-branch II medial surface with longitudinal row of small, close set spines, extending from branch 2D base, joining small spine row from sub-branch I, extending to sub-branch II apex. Sub-branch II anteriomedial surface with longitudinal row of spines. Sub-branch III with two large basomedial spines, proximal spine twice as large as distal spine. Sub-branch III posterior surface with longitudinal spine row on distal 50%. Sub-branch III apex asymmetrical, subtruncate to subangular.

Branch 2A basal 50% cylindrical, inerm ( Figs. 1A–D View Figure 1 ). Apical portion with large, proximodorsal, triangular spine, apically acute.Distal to proximodorsal spine lies transverse ridge, becoming lamellar laterally. Basal cell pad lacking. Distal portion arcuate, directed medially, apex flattened, podiform, with ventral spine. Apical margin truncate.

Second antenna ( Fig. 1A View Figure 1 )extending to thoracomere I or II. Proximal antennomere subcylindrical, posteromedial surface with rounded projection midlength. Posteromedial projection bearing small denticles, distal side sloping towards antennomere medial apex. Distomedial margin lobiform, projecting over distal antennomere base, bearing numerous denticles and scattered small setae. Distolateral margin angular, projecting slightly.Distal antennomere subequal in length to proximal antennomere; anterioposteriorly flattened, arcing gently medially approximately 20˚. Apex asymmetrical, with dorsal corner acute, ventral corner rounded.

Labrum smooth. Maxillae lobiform and transverse, no setae visible.Maxillary gland with long ventral spine, occasionally with single subdistal spinule ( Fig. 2A View Figure 2 ).

Thoracopod I endopod ( Fig. 2C View Figure 2 ) bearing single small, medial, spiniform projection. Distomedial corner triangular, bearing few filiform setae on medial margin. Distal margin deeply and broadly emarginate. Distolateral corner broadly subquadrate, lobiform, bearing distal, marginal row of four or five long spines, each separated by approximately one fourth their length, lateral margin with row of four or five short, stout spines. Proximolateral corner produced as elongated, spiniform projection, curving ventrally, apex with stout spine.

Thoracopod II endopod ( Fig.2D View Figure 2 ) broadly quadrate, lacking spines or setae. Distomedial corner acute, slightly produced distally. Distolateral corner broadly rounded.

Thoracopods III through XI serially homologous. Thoracopod V ( Fig. 2B View Figure 2 ) endites lobiform, tipped with elongate, plumose setae. Endopod subquadrate, distomedial corner produced, medial margin bearing row of short spiniform setae, distal margins with short plumose setae. Exopod ovate, margined with plumose setae, distomedial setae geniculate, with distal portions filiform and plumose. Epipodite elliptic and without marginal setae. Praepipodite broadly oval, lamellar, crenulate, without setae.

Genital segments smooth ( Fig. 2E View Figure 2 ). Retracted gonopod as for genus. Gonopod posteromedial surface with pyriform projection. Everted gonopods typical for genus.

Female. As typical for the genus. Head rounded, anterolateral corners not projecting over eyestalk base. First antenna 1.3 times length of second antenna. Second antenna broadly elliptic, lamellar. Thorax smooth. Thoracopods as in male, except first three thoracopods with endopodites not modified. Thoracopod XI with exopodite narrowly elliptic, curving dorsally, and margined with plumose setae. Brood pouch fusiform, extending to distal margin of postgenital abdominal segment IV.

Egg. ( Fig. 2F View Figure 2 ) Subspherical, diameter approximately 250 μm, with broad pentagonal or quadragonal facies, each face diameter approximately 60 μm.

Distribution and habitat. To date, D. riograndensis n. sp. is known only from the type locality ( Fig. 2G View Figure 2 ). The vicinity is primarily rice farming, which has resulted in the loss and degradation of most temporary wetlands in southern Brazil ( Volcan et al., 2015). The type locality of D. riograndensis n. sp. is an ‘island’ in the middle of rice agriculture. The site is located on a private farm that cultivates rice and cattle. The type locality is not protected, but due to the high concentration of temporary pools in the region, this species may occur at Taim ecological station (about 15 km to the north), a federal conservation unit. Presently, this species meets the criteria under the IUCN Red List (IUCN, 2001) as Critically Endangered(CR), with the area of occupancy less than 10 km 2, known only to exist at a single site (B2), and projected decline in extent of occurrence, occupancy and quality of habitat (ab).